DAMAGE BY SMOKE, ASH, AND FUMES 373 



(1) The ash from brass mills causes more or less damage to surface- 

 rooted vegetation when uniformly applied in summer over the surface 

 in amounts of 25 grams or more per square foot of surface, as shown 

 in figure 5. 



(2) When less than 25 grams arc applied per square foot of surface 

 no apparent injury takes place. 



(3) In amounts in excess of 25 grams per square foot of surface 

 the damage appears to be proportional to the amount of ash applied 

 up to 200 grams which completely kills all surface-rooted vegetation 

 within two weeks after its application. 



(4) The application of air-slaked lime in mixture with an equal 

 amount of ash completely prevents all injury even in cases where as 

 much as 200 grams of the ash is applied to one square foot of surface, 

 as shown in figure 6. 



(5) The application of air-slaked lime in mixture with an equal 

 amount of ash up to 200 grams of each per square foot of surface 

 appears to greatly stimulate growth, much more than the application 

 of the lime alone. 



From these experiments it appears that serious damage to surface- 

 rooted vegetation due to the ash (flue dust from zinc mills) can be 

 entirely overcome by keeping the soil well limed, thus preventing the 

 formation of zinc sulphate and its solution in the soil water. An in- 

 teresting outcome of the investigation is the apparent stimulating effect 

 on growth due to the application of the flue dust and lime in com- 

 bination. 



